Television



Nov. 21, 1933. J MGCREARY 1,935,650

TELEVI S ION Original Filed Jan. 5, 1928 Inuen :11"

HaruH J. PIuErearH Patented Nov. 21, 1933 TELEVISION Harold J. McCreary,Chicago, 111., assignor, by

mesne assignments, to Associated Electric Laboratories, Inc., Chicago,ill., a corporation of Delaware Original application January 3, 1928,Serial No. 244,198. Divided and this application March 11, 1930, SerialNo. 134,903.

8 Claims.

This invention relates in general to photoelectric plates, for use intelevision systems; and the object of the invention is to provide animproved photo-electric plate, and new and improved processes or methodsof constructing the same.

This application is a division of my prior application, Serial No.244,198, filed January 3, 1928, for a photo-electric plate for use intelevision systems.

The photo-electric plate forming the subject matter of this invention isdisclosed in Figs. 1 to of the drawing. Figs. 1 to 6, inclusive,illustrate in a diagrammatic manner a number of i5 forms of the plate,while Figs. 7 to 10, inclusive, illustrate two processes by which aplate of the form shown in Fig. 5 may be constructed.

Referring to Figs. 1 to 3, inclusive, 36 represents a slab of insulatingmaterial through which extend, conveniently at right angles to the hat,broad faces thereof, a large number of independent conductors 3'7.Imbedded in the faces of the slab are what may be termed grids ofconductive material, indicated respectively at 38 and 39. The elementsof these grids extend past the corresponding ends of the conductors 37but out of contact therewith, preferably so that each conductor liesbetween two grid elements. These grids form the terminals of the plate.The external circuit from grid to grid includes a battery 15 and theprimary of an induction coil, as shown in the drawing, Fig. l.

A plate of the foregoing general construction is adapted for use in atelevision transmitter of 3c the type described in my prior applicationabove referred to. As described in that application, the plate isenclosed in a cathode ray tube, in such a manner that the right-handside of the plate may be traversed or scanned by a movable cathode ray.It will be understood also that the apparatus is so arranged that animage may be focused on the left-hand side of the plate. The function ofthe plate is to produce a light current which fluctuates in value inaccordance with 40 the amount of light impinging on successivelyselected areas of the plate.

The light currents are produced by the battery 15. In order to completethe battery circuit, a conductive path must be established between atleast one of the conductors 37 and both of the grids. Any expedient maybe resorted to in order to cause a conductive path to be formed betweenone of the conductors 37 and the grid 39 when the cathode streamimpinges On the plate at the end of such conductor Renewed July 2,

(Cl. MEL-63) at the right-hand side of the plate. It the materialsemployed in the construction of the plate are not such as to produce thenecessary conductive paths between the conductors 37 and the grid 39under the influence of the cathode stream or ray, the plate may becoated with or have adjacent thereto a medium that will properly respondto the cathode ray. Thus, for example, a coating of potassium hydride,selenium, etc., may be placed on that face of the plate exposed to thecathode ray. Since the purpose of the cathode ray is simply to analyzethe plate in small sections, the conductance of the paths between theconductors 37 and the grid 39 is preferably the same at all points onthe plate; but the conductive paths on the other side of the plate mustvary in conductance according to the chosen characteristic orcharacteristics of the light in accordance with which the current ortrain of energy to be transmitted is to be modulated. The simplestmethod of securing this result is to coat that face of the plate onwhich the image is formed with potassium hydride, selenium or othersuitable material. The dotted lines 40 and 41 in Fig. 1 represent thephoto-electric media.

Selenium is a substance which changes its resistance under the influenceof light, and is well adapted for use on the image side of the plate.The coating or layer of selenium which is applied to the plate should bethin enough so that the light may produce a resistance changethroughout. In other words, the thickness of the coating must not begreater than the depth to which light will eiiectively penetrateselenium. This value is approximately .0014 cm.

The electron-emitting substances, such as potassium hydride, areespecially adapted for use on the cathode ray side of the plate, due tothe fact that the change in emission is instantaneously responsive tothe influence of the cathode ray. Because of the extreme rapidity withwhich the cathode ray scans the plate, it is desirable to use asubstance which has no appreciable slug- 100 gishness or time lag. Ifpotassium hydride is to be used, this substance may be formed on theplate by the process which is disclosed in the patent to Kunz, No.1,381,474, granted June 14, 1921. When potassium hydride is deposited in105 this manner, it forms a layer or film of minute, separate globules.

The construction of the plate which is shown in Fig. 1 can be variedconsiderably. The shape of the transverse conductors and of the gridsmay 1 be altered, and if desired, the grids may be replaced by anysuitable conductor elements which span the area of the plate, so long asthe light and the electrons of the cathode ray can reach the plate. InFigs. 4, 5, and 6, I have shown several other simple forms which theplate may have.

In the arrangement shown in Fig. 4, the bars or elements of the grids 42and 43, as well as the ends of the conductors 37, are sharp and projectbeyond the faces of the slab of insulating material. The construction isotherwise the same asin Fig. 1.

In Fig. 5, the elements or bars of the grids 43 and 44 lie spaced apartfrom the faces of the slab in which the conductors 37 are imbedded. Inthis construction, fine mesh screens may well be used as the grids, thesize of the mesh being selected to correspond with the spacing of theconductors 37, so that the interstices between the wires of the screenwill come opposite the ends of the conductors 37. The same photoelectricmaterials may be used as are described in connection with Fig. l, andthe may be applied in the same way. The right-hand grid 43, since it isseparate from the plate, will have no coating of photo-electricmaterial. The lefthand grid 44, however, should be partially imbedded inthe selenium coating, if this substance is used, so as to insure goodelectrical contact between the grid and the selenium. In case it isdesired to use potassium hydride on the image side of the plate, thecoating should be applied to the grid 44 rather than to the left face ofthe plate.

In Fig. 6, I have shown a combination of the arrangements depicted inFigs. 1 and 5, grid 38 being imbedded in the slab and the grid 43 lyingoutside the slab.

The operation of a plate of the type disclosed is explained in my priorapplication hereinbefore referred to. It will be necessary, therefore,to refer only very briefly to the particular functions which areperformed by the plate. The plate shown in Fig. 6 may be referred toconveniently, as the construction shown here is well adapted for theemployment of both types of photo-electric control; viz. by change inresistance and by change in electronic emission.

It will be assumed that a plate such as shown in Fig. 6 is suitablypositioned in a cathode ray tube, as illustrated in my priorapplication, that an image is focused on the left-hand face of theplate, and that the right-hand face of the plate is being scanned by themovable cathode ray. At the instant that the cathode ray is impinging onthe end of the upper transverse conductor 37, a circuit will becompleted as follows: From the negative pole of the battery to the grid38, thence by conduction through the selenium coating to the pin 37,through the pin 37 to the other side of the plate and to the globules ofpotassium hydride which are deposited on the end of the conductor,thence by electronic emission (caused by bombardment by the cathode ray)to the grid 43, and from the grid 43 by way of the primary of theinduction coil to the positive pole of the battery. With a givenbattery, the value of the current flow in the above circuit depends onthe electronic emission from the potassium hydride on the righthand endof the conductor 37 and on the conductivity of the selenium whichconnects the lefthand end of the conductor 37 with the grid 38. Theamount of electronic emission is constant for all of the pins 37, butthe conductivity of the cathode ray moves on and includes the nextconductor 37 in the circuit, the current flow will be over a circuitsimilar to the one traced, but the value of the current may bedifferent, due to the fact that the particular spot on the plate inwhich the active conductor 37 is located may vary as to itsillumination. It will be understood, therefore, that as the cathode rayscans the right-hand face of the plate, it includes all the conductors37 in the circuit successively, and it will be understood further thatthe amount of current flowing in the circuit each time it includes adifferent conductor 37 will depend on the illumination at the left-handend of such conductor. These varying currents constitute the so-calledlight current, which may be suitably amplified and transmitted todistant points for reproduction.

As stated hereinbefore, Figs. 7 to 10, inclusive, illustrate processesor methods by which a plate of the character described may beconveniently constructed. The plate illustrated in Fig. 5, usingseparate or detached grid elements, lends itself very well toconstruction by ordinary shop methods suitable for quantity production.

Referring to Fig. 7, one process by means of which the plates can beconstructed may be described as follows: A coil form should first beconstructed, of a size suitable to the dimensions of the plates which itis desired to manufacture. This coil form is then placed in a lathe orcoil winder, and is wound full of insulated wire. The size of the wirewill, of course, depend on the spacing desired for the transverseconductors 3'7. In practice those conductors 37 must be spaced veryclose together, so that a comparatively fine wire will have to be used.No. 28 double cotton-covered copper wire can be used with good results.As this wire is wound on the form, it is passed through a bath of liquidbakelite, otherwise known as bakelite varnish, and the insulatingcovering of the wire is thus impregnated with the bakelite compound asit is wound on the form. It is well to stop the winding operation aftereach layer has been formed for the purpose of applying additionalbakelite solution with a brush. This latter is not strictly necessary,however.

When the coil is completely wound as described in the foregoing, it isplaced in an oven. As heat is applied, the solvent is driven off, and ata certain temperature the bakelite is changed into a hard substance, ofthe familiar form, as is well understood. When removed from the oven, it

will be found that the turns of wire in the coil are all thoroughlycemented together, so that the coil has become a rigid, solid body ofthe form substantially shown in Fig. '7 of the drawing.

Plates of any desired thickness may now be cut from the coil by sawingit at the proper point. The dotted lines in Fig. '7 will illustrate howeight rectangular plates can be cut from a single coil.

After the plates have been cut out, they are again treated with abakelite solution in order to fill up any small cavities or perforationswhich may have been left due to the evaporation of the solvent. For thispurpose, some well-known form of vacuum pressure tank may be used. Afterbeing impregnated with the bakelite for a second time, the plates areagain baked in an oven, after which they may be trimmed to the requireddimensions and enclosed in suitable frames, depending on the exact formof transmitter in which they are to be used.

Figs. 8, 9, and 10 illustrate another process which may be used, ifdesired. This second process is especially desirable where it isessential to obtain a plate which is absolutely impervious to gas. Thisis not to say that the bakelite plate is not gas tight, but it is notinherently as tight as the plate about to be described.

A quantity of thin glass strips are obtained, similar to what are shownin Figs. 8 and 9. A number of these glass strips are then wound withbare wire, as illustrated in Fig. 8. After this has been done, a numberof wound strips are assembled alternately with unwound strips, asillustrated in Fig. 9, sufiicient strips of glass being used to make aplate of the desired width. The glass strips may be assembled in asuitable frame, so that they can be clamped together and held securelyin place after assembly, although a binding of wire applied at severalpoints around the outside of the complete assembly will be found to besufficient.

The assembled glass strips, which now have the form of a plate, are thenplaced in a flatbottomed crucible or other receptacle which is just alittle larger than the plate, and which forms a kind of mold. Thecrucible is then placed in a furnace, where heat is applied until theglass becomes slightly softened. During the heating of the plate, aquantity of some lowmelting type of glass should be melted upseparately. The exact type of glass is not particularly important, but Ihave found that lead borate can be used to good advantage. As soon asthe plate has been heated to the proper point in the furnace, the meltedlead borate is poured into the crucible or mold, sufficient materialbeing used so that the plate is completely covered, all the spacesbetween the diiferent glass sheets and the wires being completelyfilled. The furnace may now be closed, and a small additional amount ofheat applied to insure that the glass is all thoroughly fused togetherinto a homogeneous slab.

The furnace may now be cooled down, the glass slab being allowed to coolrather slowly, so that it will not become brittle. When the glass slabis sufliciently cool, it may be removed from the mold, after which it isplaced in a grinding machine and the two faces of the slab are groundoif to a depth of perhaps one-eighth of an inch, or enough so that allof the wire is removed except the portions which extend in a directiontransverse to the completed plate. 'I'heresult will be a rectangularslab of glass in which are imbedded a large number of fine wires. Fig.10 will give an idea of the appearance of a small section of a plateconstructed in this way.

Having described my invention, what I consider to be new and desire tohave protected by Letters Patent will be pointed out in the appendedclaims.

What is claimed is:

1. The process of constructing a photo-electric plate consisting ofinsulating material perforated by a plurality of conductors, whichconsists in winding a coil of insulated wire, in impregnating theinsulation on said wire with bakelite solution, in heating the coil toharden the bakelite,

and in cutting the coil at two points at rigfii angles to the wires toproduce the required plate 2. The process of constructing aphoto-electric plate consisting of insulating material perforated by aplurality of conductors, which consists in winding a coil of insulatedwire, in passing the wire through a bath of liquid insulating materialduring the winding operation, in heating the coil to harden theinsulating material, and cutting the coil at two points at right anglesto the wires to produce the required plate.

3. The process of constructing a photo-electric plate consisting ofinsulating material perforated by a plurality of conductors, whichconsists in winding a coil of insulated wire, in treating the insulatingmaterial to congeal the same and to thereby bind the wires tcgei'her,and in cutt ng the coil at two points at right angles to the wires toproduce the required plate.

4. The process of constructing a photo-electric plate consisting ofinsulating material perforated by a plurality of conductors, whichconsists in forming a coil of insulated wire, in impregnating the coilwith insulating material, in hardening said material, and in cutting thecoil at two points to remove the surplus material.

5. The process of constructing photo-electric plates consisting ofinsulating material perforated by a plurality of conductors, whichconsists of winding a coil of insulated wire, in impregnating the coilwith insulating material, in hardening said material, and in cutting thec011 at a plurality of points at right angles to the wires to produce anumber of the required plates.

6. The process of constructing a photo-electric plate consisting ofinsulating material perforated by a plurality of conductors, whichconsists in assembling a plurality of successive sections of a conductorin parallel spaced relation while the continuity of the conductor ismaintained, in

filling the spaces between the conductor sections with insulatingmaterial, in hardening said material, and in cutting the completeassembly in two planes at right angles to said conductor.

7. The process of constructing a photo-electric plate consisting ofinsulating material perforated by a plurality of conductors, whichconsists in forming a coil of wire in which the individual turns arespaced apart from each other, in filling the spaces between the turns ofthe coil with insulating material, in hardening said material, and incutting the coil in two planes corresponding to the two faces of thedesired plate to remove the surplus material.

8. The process of constructing a photoelectric plate consisting ofinsulating material perforated by a plurality of conductors, whichconsists in forming a plurality of conductor sections in a continuousconductor and in assembling said conductor sections in parallel spacedrelation as they are formed and while they are joined together, infilling the spaces between the conductors with insulating material, inhardening said material, and in removing all excess material lyingoutside of two parallel planes at-right angles to said conductors.

HAROLD J. McCREARY.

